1. Thermochemistry

2. Topic: Specific Heat and Calorimetry
Unit: Thermochemistry
Topic: Specific Heat and Calorimetry
Objectives: Day 1 of 3
To understand specific heat and it’s units
To understand calorimetry and and the equation q = (m)(Cp)(ΔT)
To understand the difference between endo and exothermic changes
To understand the first law of thermodynamics

3. Heat Transfer & Specific Heat
If you recall, heat is the energy transferred between objects that have different temperatures
Heat is always transferred from an object with a higher temperature to an object with a lower temperature
Temperature is a measure of the average kinetic energy

4. What is Heat?
The transfer of kinetic ______from a hotter object to a colder object
When heat is abosrbed molcules move more _______
energy
rapidly
Answer Bank
Gram
Absorbs
into
Energy
constant
Heat
system
Colder 1
transfer
Joules
rapidly

5. Heat Transfer & Specific Heat
The temperature change of an object depends on:
The amount of heat that is transferred to or from the object
The mass of the object
The specific heat of the object

6. Specific Heat
Specific heat is the amount of heat needed to raise the temperature of 1 gram of a substance by 1ºC
We represent specific heat with symbol (Cp)
It is a constant for a given substance at a certain pressure
The units of specific heat are (J/g•ºC)
Where J is the SI unit for energy, the joule (J)

7. Specific Heat
Think of specific heat as how much heat a substance can hold
Substances with a high specific heat act like a “heat sponge”
They can absorb a lot of heat with just a small change in temperature

8. What is specific heat?
The amount of ______needed to raise the temperature of 1 _____ of a substance by ___ºC
It is symbolized by the symbol Cp
It is a constant for a given substance at a certain pressure
Units are in (J/g•ºC)
heat
gram 1
Answer Bank
Gram
Absorbs
into
Energy
constant
Heat
system
Colder 1
transfer
joules

9. Calorimetry
Calorimetry is the measure of heat transfer Suppose a chemist want s to calculate the amount of heat transferred when the temperature of a sample changes by so many degrees
The amount of heat absorbed or released by a sample is symbolized by the letter q
It is calculated using the following equation: q = (m)(Cp)(ΔT)

10. What is calorimetry?
A measure of heat _______ given by the equation: q = (m)(Cp)(ΔT)
transfer
Answer Bank
Gram
Absorbs
into
Energy
constant
Heat
system
Colder 1
transfer
joules

11. q = (m)(Cp)(ΔT) Calorimetry
Here is what each symbol means for the equation: q = (m)(Cp)(ΔT)
q is the symbol for heat
If q is positive heat is absorbed
by the system & the reaction
is endothermic
M is the mass of the
sample in grams
Cp is the specific heat of the
Substance it is a constant
q = (m)(Cp)(ΔT)
If q is negative heat is lost
by the system & the reaction
is exothermic
ΔT is the change
in temperature

12. Calorimetry
If energy flows into the system (endothermic) q is positive(+)
On the other hand if energy is flowing out of the system (exothermic) q is negative(-)
Surroundings
System
Energy
Surroundings
Surroundings
Surroundings
System
Energy
Surroundings
Surroundings

13. What is the difference between endo- and exothermic changes?
An endothermic change ______ heat (q+) and energy flows ____the system
An exothermic change releases heat (q-) and energy flows out of the_____
absorbs
into
Answer Bank
Gram
Absorbs
into
Energy
constant
Heat
system
Colder 1
transfer
joules
system

14. The energy in the universe is constant
Thermodynamics
The study of energy is called thermodynamics
The law of conservation of energy is often called the first law of thermodynamics and is stated as follows:
The energy in the universe is constant

15. What is the First Law of Thermodynamics?
The First Law of Thermodynamics states that the energy in the universe is________
constant
Answer Bank
Gram
Absorbs
into
Energy
constant
Heat
system
Colder 1
transfer
joules

16. Thermodynamics The same is true for w
If the system does work on the surroundings (energy flows out of the system) w is negative
If the surrounding do work on the system (energy flows into the system) w is positive
Surroundings
Surroundings
System
System
Energy
Surroundings
Energy
Surroundings
Surroundings
Surroundings

17. Practice: Use the equation q = (m)(Cp)(ΔT) and Solve for q
What amount of heat is needed to increase the temperature of 2006 grams of Mercury (Hg) by 7.5ºC? The specific heat of mercury is J/g•ºC.
Use the equation q = (m)(Cp)(ΔT) and Solve for q
q = (m)(Cp)(ΔT)
q = (2006 g)(0.139 J/g•ºC)(7.5ºC)
q = 2090 Joules

18. First Law of Thermodynamics
The First Law of Thermodynamics states that the energy in the universe is constant
This is another way of stating the law of conservation of energy

19. The First Law of Thermodynamics
Suppose you want to measure the amount of heat transferred from a hot piece of metal (system) to a sample of cooler water (surroundings)
If you know the specific heat of water, the water’s mass and the water’s temperature change, you can calculate the amount of heat absorbed by the water
This equals the amount of heat released by the metal
System
Surroundings
System

20. Practice:
A 118 gram piece of tin at 85ºC is dropped into a 100 grams of water at 35ºC. The final temperature of the mixture is 38ºC The specific heat of water is 4.18 J/g•ºC
What amount of heat is absorbed by the water?
What amount of heat is released by the tin?
What is the specific heat of tin?
Solving for the specific heat of water we get:
q = (100g)(4.18 J/g•ºC)(3.0ºC) = 1254 J
The value is positive (+) because heat is absorbed
This same amount of heat is released by tin, and when heat is released the q value is negative (-)
qwater = -qtin
1254 J = J

21. (system surroundings)
Visualize:
What is hotter, the water or piece of tin?
In which direction will heat move?
Heat moves from the
metalTo the water
(system surroundings)
qwater Is positive (+)
heat is gained
qmetal Is negative (-)
heat is lost
100 grams of water
at 35o Celsius
System
Surroundings
118 gram piece of tin
at 85o Celsius
System

22. Practice:
A 118 gram piece of tin at 85ºC is dropped into a 100 grams of water at 35ºC. The final temperature of the mixture is 38ºC The specific heat of water is 4.18 J/g•ºC
Because the same amount of heat that is absorbed by water is also released by tin, we can use 1254 J for to solve for the amount of heat released by tin
However when heat is released, it’s value is negative and we get J, So, the amount of heat released by tin is J
Substituting in for q, we can solve for specific heat (Cp)
qtin = J = (118g)(Cp)(-47ºC)
Cp =
(118g)(-47ºC)
Cp = 0.23 J/g•ºC

23. Summarize:
In the equation, q = (m)(Cp)(ΔT), q represents the heat ____or_____, m is the ____ in grams, Cp is the _____heat, and ΔT is the change in _____
An endothermic change ______ heat (q+) and An exothermic change ______heat (q-)
In the last practice problem the amount heat lost by the ____ is equal to the amount of heat ______by the water (Or q = -q)
Answer Bank
gram
Mass
gained
Absorbs
releases
temperature
specific
metal
system
lost

24. Topic: Enthalpy and Reaction Rates
Unit: Thermochemistry
Topic: Enthalpy and Reaction Rates
Objectives: Day 2 of 2
To understand enthalpy and how it applies to a reaction
To understand how reactions proceed and the factors that effect them

25. Enthalpy
So far we have seen that some reactions are exothermic and other reactions are endothermic
Chemists also like to know exactly how much energy or heat is produced or absorbed by a given reaction
We will use the term enthalpy to describe the change in heat that occurs during a reaction
ΔH = Heat

26. Enthalpy
Enthalpy (H) is the amount of heat a sample has at a certain temperature and pressure
It is the sample’s heat content
Enthalpy cannot be measured, only changes in enthalpy can be measured
As a reaction takes place and atoms are rearranged, heat is either released or absorbed

27. What is Enthalpy?
Enthalpy (H) is the amount of ______a sample has at a certain temperature and pressure
Think of it as a sample’s heat______
heat
Answer Bank
enzyme
released
Content
activation
Absorbed
minimum
products
Heat
chemical
content

28. Enthalpy
The change in heat that takes place during a reaction is called the heat of reaction (ΔH )
It is the amount of heat released or absorbed in a chemical reaction, given 1 mol of a reactant or product
ΔHrxn is the difference between enthalpy of the reactants and products
In other words,
ΔHrxn = (H of products) – ( H of reactants)

29. What is the heat of reaction?
The amount of heat _______or _______ in a chemical reaction, given 1 mol of a reactant or product represented by ΔH
Where ΔHrxn = (H of______ ) – ( H of reactants)
absorbed
released
Answer Bank
enzyme
released
Content
activation
Absorbed
minimum
products
Heat
chemical
products

30. Practice: Classify the reactions below as wither exo- or endothermic:
CaCO3  CO2 + CaO ΔHrxn = kJ/mol CaCO3
ΔHrxn is positive so the reaction is endothermic
Reaction 2 = _______________
CH4 + 2O2  CO2 + 2H2O ΔHrxn = kJ/mol CH4
ΔHrxn is negative so the reaction is exothermic

31. The negative sign indicates an exothermic process
Practice:
When 1 mol of methane is burned at constant pressure, -890 kJ of energy is released as heat. Calculate ΔH for a process in which a 5.8 gram sample of methane is burned at constant pressure
First convert grams to moles using the
molar mass of methane 16 g/mol,
then use our conversion factor of -890 kJ/mol
q = ΔH = -890 kJ/mol CH4
The negative sign indicates an exothermic process
kJ/mol is our conversion factor
5.8 g CH4
1 mol CH4
-890kJ
= -320 kJ CH4
16.0 g CH4
1 mol CH4

32. The negative sign indicates an exothermic process
Practice:
2SO2+O2 2SO3 ΔHrxn = kJ/mol SO3
Consider the above equation:
If 8.9 mol of SO2 reacts with excess oxygen, how much heat is released?
We are given the ΔH for SO3 So, we need to use
our mol ratio to go from mol of SO2 to mol SO3
ΔHrxn = kJ/mol SO3
The negative sign indicates an exothermic process
kJ/mol is our conversion factor
8.9 mol SO2
2 mol SO3
-98.9kJ
= kJ SO3
2 mol SO2
1 mol SO3

33. Enthalpy and Reaction Rates
A change in energy always accompanies a reaction whether positive or negative
The diagram to the right illustrates how energy changes from reactants to products
The activation energy is the minimum energy needed for the reaction to take place
Once the activation energy is met, the reaction can proceed

34. Enthalpy and Reaction Rates
A common analogy is pushing a boulder over a hill. Actually over a "pass" .
The reactants are on one side like the boulder.
The energy needed to push the boulder to the crest of the hill is like the activation energy.
The products are like the condition when the boulder is at the bottom of the far side of the "pass".

35. What is Activation Energy?
The _________energy needed for the reaction to take place
minimum
Answer Bank
enzyme
released
Content
activation
Absorbed
minimum
products
Heat
chemical

36. minimum amount of energy
EA= Activation energy
minimum amount of energy
needed for a chemical
reaction to take place EA
Products
Energy ΔH
Reactants
Reaction Rate (time)
ΔH = The amount of heat
released or absorbed
in a chemical reaction
(heat change)

37. minimum amount of energy
EA= Activation energy
minimum amount of energy
needed for a chemical
reaction to take place
Products
C6H12O6 + O2 EA
ΔH = endothermic (+)
Energy
Reactants
H2O + CO2
Reaction Rate (time)

38. minimum amount of energy
EA= Activation energy
minimum amount of energy
needed for a chemical
reaction to take place
Reactants
CH4 + O2
ΔH = -890 exothermic (-)
Energy
Products
CO2 + H2O
Reaction Rate (time)

39. Catalyst
In order to lower the activation energy, some reactions utilize what’s know as a catalyst
By lowering the activation energy, a catalyst (substance) accelerates a chemical reaction without itself being affected

40. Catalyst
A catalyst is a substance that lowers the activation energy and accelerates a chemical reaction without itself being affected
A biological catalyst is called an enzyme
Enzymes help orientate molecules or atoms in specific manner so they are more likely to react
Your body has millions of enzymes!!

41. What is a catalyst?
A substance that lowers the _______energy and ________ a reaction without itself being affected or consumed in the reaction
A biological catalyst is called an _____
activation
accelerates
Answer Bank
enzyme
released
Content
activation
Absorbed
minimum
products
Heat
Chemical
accelerates
enzyme

42. Check For Understaning
Is the reaction endothermic or exothermic? 1= 2= 3= 4=
Answer Bank
Products
Activation energy
Reactants
Heat of reaction ∆H

43. Summarize:
Review:
______ is a measure of the average kinetic energy of a molecular motion
As heat is added, molecules move ______
The amount of heat released or absorbed in a chemical reaction is the _____ of reaction
A substance that lowers the activation energy is called a _____
Draw & Label the diagrams below:
Answer Bank
catalyst
faster
activation
products
Heat
temperature
Energy
Reaction Rate (time)
Reactants
H2O + C O2
Products
C6H12O6 + O2
ΔH = endothermic (+) EA
Energy
Reaction Rate (time)
Reactants
CH4 + O2
Products
CO2 + H2O
EA= Activation energy
ΔH = exothermic (-)

44. Topic: Heat Temperature & Kinetic Energy
Unit: Thermochemistry
Topic: Heat Temperature & Kinetic Energy
Objectives: Day 3 of 3
To understand the relationship between heat and kinetic energy
To understand the relationship between heat and intermolecular forces between molecules

45. Temperature and Kinetic Energy
If you recall, temperature is measure of the average kinetic energy of the atoms or molecules
In other words as heat is absorbed, molecules move more rapidly
At 0 Kelvin all molecular motion will cease

46. What is the relationship between temperature and kinetic energy of molecules???
As temperature ________, so does kinetic energy, or the _____ at which molecules move
At 0 Kelvin (-273 Co) all molecular motion will ____
increases
Answer
Bank
Increases(2)
rate
Decreases(2)
stop
rate
stop

47. Intermolecular Forces
In the solid state, molecules are held together by strong intermolecular forces
In order to overcome these forces, heat or energy must be added into the system
will occur, LIQUIDGAS
As more heat is added, intermolecular forces are overcome and a phase change occurs SOLIDLIQUID
And if even more heat is added, another phase change will occur, LIQUIDGAS

48. Intermolecular Forces
Conversely, if we remove the heat or energy, intermolecular forces will take over and the gas will become a liquid GASLIQUID
If even more heat is removed, another phase change will occur and a the liquid will become a solid LIQUIDSOLID

49. At a certain temperature (1000C) Water becomes
If we continue to add
heat, the Temperature
Of the steam will rise
At a certain temperature
(1000C) Water becomes
steam and once again the
temperature stabilizes.
Molar Heat of Vaporization
This is the
H vaporization
The energy required to
change one mol of
a liquid into vapor
The energy required
to melt 1 mole of
ice into water
At a certain temperature
(00C) the ice melts
and becomes water,
The temperature
stabilizes. This is the
Molar Heat of Fusion
H fusion
Now that the
ice has melted,
the temperature
of the water
continues to rise
Temperature
rises as we
add heat

50. What’s the relationship between heat and the intermolecular forces holding molecules together???
Answer
Bank
Increases(2)
rate
Decrease(s)(2)
stop
As a substance like water is heated, heat ______ and intermolecular forces _______.
As a substance like water is cooled, heat ______ and intermolecular forces increase.
increases
decrease
decreases

52. Empirical Formula
Empirical Formula - A formula that gives the simplest whole-number ratio of atoms in a compound.
For example:
If carbon and hydrogen are present in a compound in a ratio of 1:2, the empirical formula for the compound is CH2.

53. minimum amount of energy
Reaction Rate (time)
Reactants
H2O + C O2
Products
C6H12O6 + O2
EA= Activation energy
minimum amount of energy
needed for a chemical
reaction to take place
ΔH = endothermic (+) EA
Energy
Reaction Rate (time)
Reactants
CH4 + O2
Products
CO2 + H2O
EA= Activation energy
ΔH = -890 exothermic (-)